[Bioperl-l] parent <-> subject etc

[Chris Mungall]

On Wed, 19 Mar 2003, Hilmar Lapp wrote:

> There are different names around for the triple (actually, a quadruple
> with the namespace) making up the relationship between two vertices:
>
> 	(subject,predicate,object)
>
> or
>
> 	(child,relationship type,parent)
>
> or
>
> 	(target,relationship type,source)
>
> Some people have expressed in the past that some of these depictions
> are inferior to others for some reason or another, which quite frankly
> I don't agree with (e.g., subject/predicate/object may make a lot of
> sense for ontology terms, but not really for feature graphs). To me

for containment graphs or is-a inheritance graphs, the semantics of
'parent' vs 'child' is obvious, but this is not the case for other kinds
of graph. using subject/object there is no potential for ambiguity.

> it's mostly a matter of taste, consistency, and documentation to make
> sure the directionality doesn't get confused (feature graphs,
> bioentry-bioentry relationships, and term-term relationships are all
> directed).
>
> So, just to be sure I'm not confused already, if I define that the last
> (3rd) element in the aforementioned tuples has the smaller distance to
> the root along the 1st element's path to the root, then the order of
> elements above depicts the equivalent designations, right?

if you're asking if they are all equivalent, yes. ie child=subject

i think it's wrong to thing in terms of graphs that are always rooted -
what about cyclical graphs?

> Once we all agree on this I'll document it in RelationshipI and the
> biosql schema.
>
> 	-hilmar
>